[PATCH v5 10/20] KVM: x86: Support EGPR accessing and tracking for emulator

[Chang S. Bae]

Extend the emulator context and GPR accessors to handle EGPRs before
adding support for REX2-prefixed instructions. Like VCPU cache, the
emulator can uniformly cache and track all GPRs.

Also replace `1 << reg` with `BIT(reg)` in reg_read()/reg_write(). The
former performs a signed 32-bit shift, which becomes undefined for R31.
BIT() instead shifts an unsigned value that is suitable for all indices.

Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
---
V4 -> V5: Fix possible shift-out-of-bounds (review bot [*])

[*]: locally running Sashiko with gemini-3.1-pro-preview
---
 arch/x86/kvm/kvm_emulate.h | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index 3e375af15c03..b1498f618c81 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -109,13 +109,13 @@ struct x86_instruction_info {
 struct x86_emulate_ops {
 	void (*vm_bugged)(struct x86_emulate_ctxt *ctxt);
 	/*
-	 * read_gpr: read a general purpose register (rax - r15)
+	 * read_gpr: read a general purpose register (rax - r31)
 	 *
 	 * @reg: gpr number.
 	 */
 	ulong (*read_gpr)(struct x86_emulate_ctxt *ctxt, unsigned reg);
 	/*
-	 * write_gpr: write a general purpose register (rax - r15)
+	 * write_gpr: write a general purpose register (rax - r31)
 	 *
 	 * @reg: gpr number.
 	 * @val: value to write.
@@ -321,7 +321,9 @@ typedef void (*fastop_t)(struct fastop *);
  * also uses _eip, RIP cannot be a register operand nor can it be an operand in
  * a ModRM or SIB byte.
  */
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_KVM_APX)
+#define NR_EMULATOR_GPRS	32
+#elif defined(CONFIG_X86_64)
 #define NR_EMULATOR_GPRS	16
 #else
 #define NR_EMULATOR_GPRS	8
@@ -381,9 +383,9 @@ struct x86_emulate_ctxt {
 	u8 lock_prefix;
 	u8 rep_prefix;
 	/* bitmaps of registers in _regs[] that can be read */
-	u16 regs_valid;
+	u32 regs_valid;
 	/* bitmaps of registers in _regs[] that have been written */
-	u16 regs_dirty;
+	u32 regs_dirty;
 	/* modrm */
 	u8 modrm;
 	u8 modrm_mod;
@@ -547,8 +549,8 @@ static inline ulong reg_read(struct x86_emulate_ctxt *ctxt, unsigned nr)
 	if (KVM_EMULATOR_BUG_ON(nr >= NR_EMULATOR_GPRS, ctxt))
 		nr &= NR_EMULATOR_GPRS - 1;
 
-	if (!(ctxt->regs_valid & (1 << nr))) {
-		ctxt->regs_valid |= 1 << nr;
+	if (!(ctxt->regs_valid & BIT(nr))) {
+		ctxt->regs_valid |= BIT(nr);
 		ctxt->_regs[nr] = ctxt->ops->read_gpr(ctxt, nr);
 	}
 	return ctxt->_regs[nr];
@@ -562,8 +564,8 @@ static inline ulong *reg_write(struct x86_emulate_ctxt *ctxt, unsigned nr)
 	BUILD_BUG_ON(sizeof(ctxt->regs_dirty) * BITS_PER_BYTE < NR_EMULATOR_GPRS);
 	BUILD_BUG_ON(sizeof(ctxt->regs_valid) * BITS_PER_BYTE < NR_EMULATOR_GPRS);
 
-	ctxt->regs_valid |= 1 << nr;
-	ctxt->regs_dirty |= 1 << nr;
+	ctxt->regs_valid |= BIT(nr);
+	ctxt->regs_dirty |= BIT(nr);
 	return &ctxt->_regs[nr];
 }
 
-- 
2.53.0